This invention relates to improvements in the paper feed device for duplicators.
Paper feed devices for electronic duplicators are mostly based upon cassette paper supply from paper feed cassette.
However, with a device which is designed to permit only cassette paper supply, inconvenience is felt in case when it is desired to manually supply a paper sheet of a different size from that of paper accommodated in the paper feed cassette.
Accordingly, it has been proposed to provide the duplicator with two separate exclusive paper feed devices for cassette paper supply and manual paper supply so that paper can be readily supplied in either cassette or manual paper supply mode. However, where such two separate paper feed devices are used, a detection switch system for detecting the absence of paper in the paper feed cassette and a detection switch system for detecting the passage of paper in case of the manual paper supply are needed. Such detection switch systems require extra space and increase the size of the paper feed system as well as complicating the paper feed system with wirings involved.
In another aspect, with duplicators for use with paper feed cassette as mentioned above, the paper feed system is usually constituted by a plurality of paper feed mechanisms provided in the duplicator, and paper feed cassettes accommodating paper sheets of different sizes, for instance, A4, B4 and B5 sizes, are loaded in paper feed sections of the respective paper feed mechanisms so that cassette paper sheets of desired sizes can be automatically supplied by operating the corresponding paper feed mechanisms. In some duplicators where a plurality of paper feed cassettes are loaded for use, there is a trend of loading a plurality of cassettes accommodating paper of the size of frequent use in order to save time required for renewing cassette and obtain as efficient copying operation as possible.
However, as is well known in the art, the paper feed systems for such duplicators are constructed such that paper supply is automatically stopped when the cassette in use has run out of paper sheets. This occurs even if other cassettes accommodating paper of the same size are loaded in the duplicator. If this occurs while operator has left the duplicator on an errand by thinking that he would return by the time when the scheduled copying operation is over, the copying will not be ended as scheduled, which is disadvantageous.
In a further aspect, in the electronic duplicator it is usual to make optical scanning of original document, on-off control of charging or development according to the length of the copying paper sheet. The length of the copying paper sheet is usually detected through the detection of the trailing edge of paper sheet being transported, for instance by a detecting means provided in the paper transport path of the paper feed device. FIGS. 1 and 2 show examples of the prior-art paper feed device provided with a detecting means.
The detecting means shown in FIG. 1 comprises an actuator 4 provided in the paper transport path 2 and a detection switch 6 provided near the path 2 on either side thereof and coupled to the actuator 4 by a rotatable member 8. The actuator 4 is adapted to be operated, for instance swung up or down, by a copying paper sheet being fed into the transport path 2, and the passage of the trailing edge of the paper sheet 10 by the actuator is detected by the detection switch 6. In the Figure, designated at 12 is a paper feed cassette, at 14 upper and lower guides constituting the paper transport path, and at 16 a paper feed roller unit.
The detecting means shown in FIG. 2 comprises photoelectric cells 18 disposed on the upper and lower sides of paper transport path 2 in vertical alignment to each other. With this arrangement, the trailing edge of copying paper sheet 10 being fed to the paper transport path 2 is detected in terms of whether light is transmitted through the paper transport path. In FIGS. 1 and 2 like parts are designated by like reference numerals, and redundant description is dispensed with.
However, in order for such detecting means with the detecting section provided in the paper transport path 2 to be able to detect the trailing edge of the paper sheet 10, the detecting section has to be disposed such that the distance between it and a transfer section is greater than the distance between a photosensitive drum charger and the transfer section along the photosensitive drum. This means that the provision of the detecting section is impossible with a small-size duplicator provided with a paper transport path where the distance between the paper feed section and transfer section is too small.
In the detecting means having the actuator 4 as shown in FIG. 1 disposed on the paper feed path 2, jamming tends to occur in the supply of the copying paper and thus a smooth paper supply of the copying paper is prevented. A detecting means disposing photoelectric elements 18, 18 (see FIG. 2) on a paper feed path 2 provides no "jamming" problem, but when it is desired to detect a copying paper 10 of, for example, a thin type having a higher degree of transparency to light, difficulty is encountered in detecting the trailing edge of the copying paper.
Further, where a plurality of paper feed cassettes are provided, it is necessary to provide a corresponding number of detecting sections with the aforementioned constructions of the detecting means with the detecting section disposed in a predetermined position of the paper transport path 2, which leads to complications of the detecting system.
In a still another aspect, in case of the paper feed device which is capable of permitting paper supply in a cassette paper supply mode and also in a manual paper supply mode, a manual paper supply door is provided, the cassette paper supply mode or manual paper supply mode can be selectively obtained by opening or closing this door. With this type of paper feed device, the door is closed or opened to recover the cassette paper supply mode after the manual supply of paper is ended. However, it is often the case that the door is left in its state of manual paper supply even after the end thereof, and this leads to the malfunction of causing copying operation by cassette paper supply while the cassette paper supply mode is not recovered.
As for further prior-art, Japanese Patent Publication No. 50-1210, N. Yanagawa, Jan. 16, 1975, discloses "automatic paper supply cut-off device in manual paper supply in duplicator provided with cassette paper feed device and repeat mechanism". This disclosure teaches that in a duplicator of automatic paper supply type provided with a cassette paper feed device and a repeat mechanism, in which automatic cassette paper supply is interrupted to permit manual paper supply even with the operation of a manual paper sheet length detection switch.
Also, Japanese Patent Application No. 54-16108, S. Komori et al, June 20, 1979, entitled "Paper Feed Cassette Device" discloses a paper feed cassette device, which comprises a paper feed cassette accommodating paper sheets, a paper feed means for feeding paper sheets from the cassette and a manual paper supply table for manually feeding a paper sheet different from those accommodated in the cassette, and in which the paper feed means can feed the different paper sheet supplied from the manual paper supply table as well.
Further, Japanese Patent Publication No. 54-24788, Y. Hatanaka et al, Aug. 23, 1979, entitled "Method of and Device for Detecting Jamming of Sheets", discloses method of and device for accurately detecting jamming irrespective of the position of sheet being transported.
However, none of the above disclosures contains a construction capable of automatically switching a manual paper supply mode over to a cassette paper supply mode in response to the end of manual paper supply.